The overall goal is to determine the relationship between modulation of TL antigenicity from mouse thymocytes and leukemia cells and changes in the organization of TL antigens within the cell surface. Specifically, the molecular nature of a serum factor affecting complement lysis of TL antigen-antibody complexes will be investigated, as well as the manner of action of this factor. Efforts will continue to determine the role of microfilaments and microtubules in controlling the mobility characteristics of TL antigens, and the relationship between alterations in antigen mobility and intracellular cyclic nucleotide levels. The relationship between phenotypic expression of TL antigens and other surface antigens will be assessed by radioisotope labeling procedures.